Glioblastoma multiforme (GBM) is one of the most lethal malignancies in part due to its highly invasive nature and due to the relative resistance of GBM cells to fully respond to radio- or chemo-therapies. A series of compounds have been derived from the chemical backbone of the NSAID Celecoxib that do not possess COX2 inhibitory activity, but are highly bio-available, can cross the blood-brain barrier, and are an order of magnitude more potent at suppressing tumor cell viability than the parent drug. We have shown that the most potent lead compound, OSU-03012, causes a strong induction cell death in established and primary human GBM cells in vitro, but not in cultures of non-transformed primary astrocytes or primary hepatocytes, at concentrations in the 1-5 M range, which is lower than the 15-20 M achievable plasma concentration of this agent in rodents. This compound was selected by the NCI RAID program for development, in part based on our data, and a phase I trial with this drug as a single agent will commence in other tumor types in 2009. We have demonstrated in primary and established human GBM cells that OSU-03012 suppresses short-term viability and colony formation in vitro and that OSU-03012 -induced killing occurs primarily via in the induction of a toxic endoplasmic reticulum (ER) stress / autophagy signal. In vivo we have noted in one GBM model that OSU-03012 can enhance animal survival and interact with radiotherapy to further prolong survival. We have published that the lethality of OSU-03012 is magnified by inhibition of HSP90 or by exposure to ionizing radiation. We hypothesize that: geldanamycin HSP90 agonists via ROS and ceramide production cause CD95 activation in parallel to OSU-03012 -induced toxic autophagy which is responsible for the synergy of GBM cell killing. We hypothesize that: ionizing radiation enhances OSU-03012 toxicity by promoting expression/ activation of ceramide synthase genes which enhances OSU-03012 -induced toxic autophagy. Specific Aim 1: Will determine the molecular mechanism(s) by which OSU-03012 toxicity in primary human GBM cells is promoted by exposure to the HSP90 antagonists (geldanamycins) 17AAG / 17DMAG. Specific Aim 2: Will determine the molecular mechanisms by which OSU-03012 radio-sensitizes primary human GBM cells with specific focus on the regulatory roles of ceramide synthase genes. Specific Aim 3: Will determine, using orthotopic xenograft models of primary human GBM cells, whether OSU-03012 enhances the tumoricidal effects of ionizing radiation or of 17AAG, in vivo. The goal of the studies in this proposal is to provide detailed mechanistic evidence to move OSU-03012 as a therapeutic for GBM from the bench into the clinic.